Secrecy intercommunicating telephone system



W. H. WAITE Nov. 28, 1939.

SBCRECY INTERCOMMUNICATING TELEPHONE SYSTEM Filed Jan. 15, 1938 2Sueta-Shqet 1 l H INVENTOR BY 1 A AT RNE Nov. 28, 1939. w, w rrE2,181,715

SECRECY INTERCOMMUNICATING TELEPHONE SYSTEM Filed Jan. 13, 1938 2Sheets-Sheet 2 a" fig? (Wyn;

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o o o Patented Nov. 28, 1939 UNITED STATES PATENT OFFIC SECBEUYINTEBCOMMUNTCATING TELE- PHONE SYSTEM William H. Waite, Lynbrook, N. Yassignor to Dictograph Products Company,

Inc., New

This invention relates to an intercommunicat-.

- =ing telephone system in which complete secrecy of conversation ismaintained between any two communicating stations.

I A conventional intercommunicating telephone system comprises a numberof stations, each connected to its own pair of talking wires, and eachequipped with a plurality of keys or switchees by means of which thetelephone receiver and transmitter at any station can be connected tothe pair of talking wires corresponding to any other station. Additionalcommon wires are required to supply voltage from the talking andsignalling batteries to their respective circuits. In the ma- 1B jorityof such systems, no provision is made for secrecy of communicationbetween any two stations, so that it is possible for a third station tobe connected to one of two communicating stations. Other systems whichprovide for secrecy 01 communication are not positive in their action,as in the case where the connection between two stations is contingentupon the ability of -.the calling station to operate the buzzer oraudible signal at the called station.

25, In accordance with this invention a secrecy intercommunicatingtelephone system is provided which utilizes a control relay connected inparallel with the pair of talking wires of the called station, whichoperates in one of two ways, de-

pending on the condition of the talking wires.

If the called line is not in use, the second station can be signalledand the talking circuit closed. If the called line is busy, however, anaudible signal operates at the calling station,

notifying the operator at that station of the condition of the line, andat the same time making it impossible for him to close the talkingcircuit to the busy station.

Also, energization of the talking circuit to any substation energizesthe audible signal at that station, provided that the switch at thatstation is closed, or, alternatively, if the telephone receiverthereoiis on its hook.

In the preferred embodiment of this invention,

the operator at one station desiring to call a second station removeshis receiver from its hook and manipulates the key corresponding to thedesired station. This connects the control relay, directly across thepair of wires of the called line. If the line is not in use, thiscontrol relay is not energized, and in this position it completes acircuit to a second relay, hereinafter called the line relay, through aringing key. The operation of the ringing key applies part of the voltasage of the talking battery 350 this line relay,

thereby closing its contacts. The line relay is equipped with amechanical latch so that once it has been energized, its contacts willremain closed until the latch is released by the replacement of thereceiver at the calling station on its 6 hook, or by the manipulation ofanother calling key at the calling station. The operation of the linerelay connects the telephone instrument of the calling station to thepair of talking wires corresponding to the called station, thus con- 10necting these wires to the talking battery, and energizing a relay atthe called station. This last relay completes a circuit through theaudible signal and the signalling battery, its sound indicating that thestation is being called. The operator thereupon removes his receiverfrom its hook and the conversation may begin.

In the case where the called line is initially busy, the control relayis energized the instant that the key is operated at the callingstation. 20

' When the ringing key is then actuated. a circuit is completed,energizing a signal or buzzer relay at the calling station, and thesound of the buzzer indicates to the caller that the called line isbusy. The control relay remains closed as long 25 as the called line isbusy, and in this position it is impossible for the line relay tooperate and connect the calling station telephone instrument to the busyline.

It will be seen that the new system of this invention provides theadvantages of simplicity of previous systems, and in addition providesfor absolute secrecy of interstation conversations without complicatingoperations or apparatus.

For a more complete understanding of the invention, reference may be hadto the accompanying drawings, in which:

Figure 1 is a schematic diagram illustrating an embodiment of theinvention;

Fig. 2 is a simplified diagram of the elementary telephone circuit uponwhich this invention is based; and

Fig. 3 illustrates a mechanical arrangement for holding the line relayclosed after it has once 45 been energized.

While the system can be adapted to include any number of stations, onlytwo stations, A and B, are shown in Fig. -1, since their method ofoperation is identical with that of any other two 50 stations of thesystem.

Each station comprises the usual receiver l0 and a microphone ortransmitter II, a switch l2 actuated by the receiver hook I3, a key orswitch i4 corresponding to each 01. the other stations in the system, acontrol relay I5, a line relay and a signal relay I1.

. The key or switch I4 consists of four contact springs, of which thefirst spring I8 is normally disengaged from the second spring I9, andthe third spring 20 is normally disengaged from the fourth spring 2|. Aninsulating bar! 22 between the springs I9 and 2| causes them to move asa unit.

Considering station A, thefirst spring I8 is connected by wire 23 tocommon talking wire 24, and third spring 28 is connected by wire 25 tothe second common talking wire 28. Second spring I9 is connected by wire28' to a spring contact 21 on the line relay I8, and by wire 54 throughcontrol relay I5and wires 55 and 28 to fourth spring 2| of key I4, whichis also connected to contact 29 of line relay I8.

Normally disengaged from relay contact 21 is contact spring 38,mechanically connected to but insulated from the armature'3l oi linerelay I8. The armature 3| is also mechanically connected to butinsulated from contact spring 33, which normally engages a springcontact 34. Between the spring 33 and a spring 35 is an insulating block38 adapted to move spring 35 into engagement with contact 29 as therelay I8 is energized. Control relay I5 armature 58 normally engagescontact 51 connected by wire 83 through line relay I8 and wires 84 and4| to negative common wire 42. I

Contact spring 33 of line relay I8 is connected by wire 19 to contact18, which is normally disengaged from armature 58 of con'trol relay I5,the armature 58 being connected by wire 82 through normally open rin ingkey 58 and wires 59 and 41'to common pos tive wire 48.

Receiver switch I2 comprises three spring contacts and the receiver hookI 3. The first spring 31 is part of the talking circuit, and isconnected through resistor 38, receiver I9 and the microphone or transmtter II, wire 39, impedance coil 48, and a wire 4| to the negative linewire 42, which is connected to the negative terminal of the talkingbattery 43.

The second spring 44 of switch I2 is connected. through wire 45,impedance coil 48, and wire 41 to the positive line wire 48, which isconnected to thepos tive terminal of the talking battery 43.

The receiver hook I3 01 the switch I2 is connected through wire 49 totalking wire 59 of station A and by wires 49 and 5| to the spring 35 onthe line relay I8.

Atstation B the receiver hook I3 is connected by wire 5'! to the talkingwire 28. and, as before,

. wire 5| connects the wire 52 with the spring 35 of the line relay I8.

The lower contact of receiver switch I2 normally engages hook I3 and isconnected to contact 34 of line relay I6 and by wire 81 through signalrelay I1, and wires 88 and 4| to common. negative signal wire 42. Thearmature 89 of signal relay I1 is connected by wire to common negativesignal wire 14 and, when actuated, engages contact 10 to complete thelocal signal circuit through buzzer 1| and impedance 12 t commonpositive signal wire 13.

In operation, when the party at station A desires to communicate withstation B, he removes his receiver Ill from its hook I3, thus causinghook I3 to disengage contact 85 and engage contact 44, which is causedto engage contact 31. He then manipulates the key switch I4corresponding to station B to engage contacts I8, I9, and 20, 2|. Thiscompletes a circuit 1 7cm common-wire 24, wire 23, contacts I8 and I9,

wire 54, the control relay I5, wire 55, contacts 2| and 20, wire 25 andcommon talking wire 28. I1 station B is not busy, there is no voltageacross the wires 24 and 28, and control relay I5 will not be energizedand its armature 58 will remain engazed with contact 51. Actuation oithe ringing key 58 closes a circuit from common positive line 48 oi thetalking battery 43, wires 41 and 59, closed contacts 80 and BI of theringing key 58, wire 82, armature 58 of the control relay I8 engagingcontact 51, wire 83, line relay I8 and wires 84 and 4| to commonnegative wire 42 of the talking battery 43. The armature 3| oi energizedline relay I8 is maintained in the raised position by a mechanicallatch, which will be described later.

The closed contacts of energized line relay I8 complete a signallingcircuit between station A and station B traceable at station A fromcommon positive line 48, wire 41, impedance coil 48, wire 45, contact 44engaging the receiver hook I3, wires 49 and 5|, closed line relaycontacts 35 and 29, wire 28, closed key, contacts 2| and 28, wire 25,common talking wire 28 to station B, wire 52, receiver hook I3 engagingcontact 85, wire 81, signal relay I1 and wires 88 and 4| to commonnegative line 42. This completes the station B signal circuit fromcommon negative wire 14 01' the signalling battery 18, wire 15,armature;

89 of signal relay I1 engaging the spring contact 18,- buzzer 1|,protective resistor 12, to common positive line13 of the signallingbattery 18. The buzzer indicates to the party at station B that he isbeing called and the buzzer signal is maintained until the receiver I0is removed from the hook I3 of station B, when the buzzer circuit isbroken by the disengagement of the spring contact 85 with the receiverhook I3.

The removal of the receiver from its hook at station B releases thereceiver hook I3 to cause engagement of contacts 44 and 31, thuscompleting the talking circuit between the two stations, which istraceable at station A from common talking wire 24, wire 23, contacts I8and I9 of key I4, wire 28', contacts 21 and 38 of the line relay I8,wire 39, station A microphone or transmitter I I, receiver I0,protective resistor 38, con

tact 31, contact 44 engaging the receiver hook I3, wires 49 and 5|,contacts 29 and 35 of the line relay l8, wire 28, contacts 2| and of thekey I4 and wire to common talking wire 28.. From common talking wire 28the'talking circuit is traced to wire 52 at station B, receiver hook I3engaging contact 44, contact 31, protective resistor 38, receiver I0,microphone or transmitter II, wires 39 and 24.

The positive terminal of the talking battery 43 is connected to thetalking circuit at both station A and station B through common positiveline wire 48, wire 41, impedance coil 48, wire 45 and the engagedreceiver switch I2 contacts 31 and 44. The negative terminal of thetalking battery 43 is also connected to the talking circuit at bothstations through common negative line 11 back to common talking wire 42,wire 4|, impedance coil 40 and wire 39 to the microphone or transmitterII.

Fig. 2 is a simplified diagram of the talking circuit. The impedancecoils 40 and 48 do not retard direct current to the talking circuit, butprevent the passage of voice currents through the talking battery 43.The impedance of the talking circuit is made low with respect to that oftheimpedance coils 40 and 48 to insure that most of the voice currentwill circulate between the telephone instruments of the stations andlittle or none will pass through the common talking battery 43. Thistends to reduce the possibility of cross talk where a number ofconversations take place between diflerent stations simultaneously, andthus helps to maintain complete secrecy or communication.

In the case where station B is initially busy, the voltage of thetalking battery 43 is impressed across the lines 24 and 28 so that thecontrol relay I8 is energized the instant that the key 4 is manipulated.Its armature 86 engages the contact 18, thus closing a circuit throughthe ringing key 58. When this key 58 is actuated, the voltage of thetalking battery 43 is applied through common negative wire 48, wires 41and 89, the engaged contacts 88 and 8| of the ringing key 58, wire 62,armature 58 of the control relay I8 engaging contact 18, wire 19,normally engaged contacts 33 and 34 of the line relay I8, wire 81,signal relay l1 and wires 88 and-4| to common positive line 42. Thearmature 69 of signal relay l'l engages contact 18, thus energizing thelocal buzzer 1|. The buzzer signal accordingly is an indication to thecalling party at station A that station B is busy. It should be observedthat as long as station E is busy, it is impossible to energize the linerelay l8 and thus connect the telephone instruments at station A to thetalking wires corresponding to station B, whereby absolute secrecy ismaintained.

The mechanical latch for holding the armature 3| of the line relay It inthe raised position is illustrated in Fig. 3 and may be an adaptation ofthe latch disclosed in Koch Patent No. 2,003,- 689. The receiver hook I3is illustrated as oi. the cradle type' for receiving combined receiverand transmitter handset. The weight of the handset on the receiver hookI3 is transmitted by rod 88 to a bell crank 8|, 83, which is pivoted at82. The end 84 of arm 83 engages arm 85 on the locking bar 86 having abell crank 81 pivoted at 88 and connected to the end of a thrust rod 89,which is slotted to receive a fixed pin 90, and bears on a latch 9|pivoted at 92 and held in contact with the thrust rod 89 by lighttension spring 93 connected at opposite ends 94 and 95 to the respectivethrust rod 89 and latch 9|.

When the handset is removed from the hook or cradle I3, the usualspring, not shown, raises |3 until arm 8| engages the stop 96 todisengage the end 84 of arm 83 from arm 85 so that its end 86 drops inposition for engagement in one of the notches 99 when pivoted switch keyM is manipulated. The thrust rod 89 is thus raised slightly, so thatwhen the line relay I6 is energized, its armature 3| engages the notchIM and is locked in this position by the latch 9|.

The latch 9| is released either by replacing the handset on the receiverhook or cradle I3,

or by manipulating one of the keys M. In the former case, thrust rod 89drops, disengaging latch 9| from the armature 3| to release it. In

the latter case, the manipulation of a key I4 I claim:

1. In a telephone system, the combination of a plurality of stationseach having a telephone instrument, talking lines interconnecting saidinstruments, 9. switch at each station for energizing the talking lineof a selected other station, a control relay across-said talking line ateach local station responsive to previous energization of a talking lineby a remote station switch upon actuation of the corresponding localswitch calling said last-named remote station, and a connection to thesaid last-named local station telephone instrument controlled by saidrelay whereby communication between said lastnamed local stationtelephone instrument and said last-named remote station telephoneinstrument is prevented while the latter remains busy.

2. In a telephone system, the combination of a plurality of stations,each having a telephone instrument, talking lines interconnecting saidinstruments, a switch at each station for energizing the talking line ofa selected other station, a control relay across said talking line ateach local station responsive to previous energization of a talking lineby a remote station switch upon actuation of the corresponding localswitch calling said last-named remote station, connections to the saidlast-named local station telephone instrument controlled by said relaywhereby communication between said last-named local station telephoneinstrument and said last-named remote station telephone instrument isprevented while the latter remains busy, and a signal at said last-namedlocal station controlled by said relay for indicating that the calledlast-named remote station is busy.

3. In a telephone system, the combination of a plurality of stations,each having a telephone instrument, talking lines interconnecting saidinstruments, a switch at each station for connecting the correspondingtalking line to a remote station instrument, and a control relay at eachstation across the corresponding talking line responsive to previousenergization of the talking line of a selected remote station fordisabling the local station telephone instrument while the talking lineof the selected remote station remains energized.

4. In a telephone system, the combination of a plurality of stations,each having a telephone instrument, talking lines interconnecting saidinstruments, a switch at each station for connecting the correspondingtalking line to a remote station instrument, a control relay at eachstation across the corresponding talking line responsive to previousenergization of the talking line of a selected remote station fordisabling the local station telephone instrument while the talking lineof the selected remote station remains energized, and a signal at saidlast-named local station controlled by said relay for indicating thatthe selected remote station is busy.

5. In a telephone system, the combination of a plurality of stationseach having telephone instruments, talking lines interconnecting saidstations, 2. switch at each station for connecting the correspondingline to a selected remote station, a local control relay at each stationacross the corresponding talking line, normally closed contacts on saidrelay preparing a talking circuit to a remote station selected by thecorresponding switch, and second contacts on said relay disiiigizationof the selected remote station talking line.

6. In a telephone system, the combination of a plurality of stationseach having telephone in struments, talking lines interconnecting saidstations, a switch at each station for connecting the corresponding lineto a selected remote station, a local control relay at each stationacross the corresponding talking line, normally closed contacts on saidrelay preparing a talking circuit to a remote station selected by thecorresponding switch, second contacts on said relay disabling the localstation instrument upon actuation of said relay in response to previousenergization of the selected remote station talking line, and a signalat said local station responsive to energization of said relay forindicating that the selected remote station is busy.

7. In a telephone system, the combination of a plurality of stationseach having a telephone instrument, talking lines interconnecting saidinstruments, a line relay at each station controlling the correspondingtalking line to a selected remote station, a switch at each stationcontrolling alarms sponding talking line responsive to previousenergization oi the remote station instrument selected by said switchfor disabling the corresponding line relay while the selected remotestation re'- mains busy, and a signal at the talking stationresponsive-to energization of said control relay lillor indicating thatthe called remote station is 9. In a telephone system, the combinationof a plurality of stations each having a telephone instrument, talkinglines interconnecting said instruments, a line relay at each stationcontrolling the corresponding talking line to a selected remote station,a switch at each station controlling said relay, a control relay acrosssaid corresponding talking line responsive to previous ener gization ofthe remote station instrument selected by said switch {or disabling thecorresponding line relay while the selected remote station remains busy,a signal relay at the calling station responsive to actuation of saidcontrol relay, and a signal actuated by said signal relay to indicatethat the called station is busy.

10. In a telephone system, the combination of a plurality of stationseach having a telephone instrument, talking lines interconnecting saidinstruments, a line relay at each station, a switch at each station forenergizing the corresponding line relay to connect the correspondinglocal telephone instrument to the talking line of a selected remotestation, and a control switch interposed between said first switch andline relay actuated by said control relay to disable said line relay inresponse to previous energization of the talking line of said selectedremote stations.

WILLIAM H. WAI'I'E.

